- Total Energy Expenditure (TEE), or the total number or calories we use in a day has many components, and exercise is only a tiny, tiny part
- Basal Metabolic Rate, Thermogenic effect of Food, Non-Exercise activity thermogenesis, excess post-exercise oxygen consumption and exercise all contribute to TEE
- Compensation limits the weight loss effect of exercise
- Exercise usually increases food intake
- Exercise often does not increase daily overall activity because it tends to decrease non-exercise movement
By Jason Fung, M.D., Co-founder of The Fasting Method
Exercise is often (wrongly) assumed to be extremely important for weight loss as depicted in many popular shows such as ‘The Biggest Loser’. But science says otherwise. A recent scientific review notes that “You can’t outrun a bad diet”, meaning that exercise, while healthy in many ways, is a terribly inefficient method of weight loss. The reason for this common error lies in the misunderstanding of how many calories are used daily, or Total Energy Expenditure (TEE) or ‘Calories Out’ part of the Energy Balance Equation:
Fat gained = Calories In - Calories Out
Sometimes nutritionists call upon the First Law of Thermodynamics, that energy in a closed system is neither gained nor lost as ‘proof’ of the primacy of calorie theory. It’s funny how nutritionists always reference thermodynamics, drawn to as children to amusement parks, but physicists who spend decades studying thermodynamics never, never, never talk about calories and weight loss. Calorie-enthusiasts want to pretend that nutrition, too, is a ‘hard science’ like physics with ‘inviolable’ laws. Sad, and more than a little pathetic. Any who…
A superficial look at this equation suggests that increasing daily calorie expenditure leads to fat loss. ‘Calories Out’ is more accurately termed total energy expenditure (TEE) – the sum of basal metabolic rate (BMR), thermogenic effect of food (TEF), non-exercise activity thermogenesis (NEAT), excess post-exercise oxygen consumption (EPOC) and, of course, exercise.
TEE = BMR + TEF + NEAT + EPOC + Exercise
The key point here is that TEE is not the same as exercise. The overwhelming majority of TEE is not exercise but the BMR: metabolic housekeeping tasks such as breathing, maintaining body temperature, keeping the heart pumping, maintaining the vital organs, brain function, liver function, kidney function, etc. This is the energy needed for all of the body to function normally, and happens without any type of conscious control.
Let’s take an example. BMR for a lightly active average male is roughly 2500 calories per day. Walking at a moderate pace (two miles per hour) for forty-five minutes every day, would burn roughly 104 calories. In other words, that will not even consume 5 percent of the TEE. The vast majority (95 percent) of calories are used for all the other organs needed to stay alive.
NEAT is the energy used in activity other than sleeping, eating or exercise; for instance, in walking, gardening, cooking, cleaning and shopping. TEF is the energy used in digestion and absorption of food energy. Certain foods, such as dietary fat, are easily absorbed and take very little energy to metabolize. Proteins are harder to process and use more energy. TEF varies according to meal size, meal frequency and macronutrient composition. Excess post-exercise oxygen consumption (EPOC—also called after-burn) is the energy used in cellular repair, replenishment of fuel stores and other recovery activities after exercise.
Generally, NEAT, TEF and EPOC are ignored because they are relatively small, and relatively constant over time. However, many also assume that the largest contributor to TEE, namely BMR also stays constant over time, and therefore the only factor that changes is exercise. This is absolutely false. BMR varies depends on many factors, including
- gender (BMR is generally higher in men),
- age (BMR generally drops with age),
- weight (BMR generally increases with muscle mass),
- height (BMR generally increases with height),
- diet (overfeeding or underfeeding),
- body temperature,
- external temperature (heating or cooling the body) and
- organ function.
Decreased caloric intake can decrease BMR by up to 40 percent. Increased caloric intake can increase it by 50 percent. What determines the energy output of the system? Suppose we consume 2,000 calories of chemical energy (food) in one day. What is the metabolic fate of those 2,000 calories? Possibilities for their use include
- heat production,
- new protein production,
- new bone production,
- new muscle production,
- cognition (brain),
- increased heart rate (heart),
- increased stroke volume (heart),
- exercise/physical exertion,
- detoxification (liver),
- detoxification (kidney),
- digestion (pancreas and bowels),
- breathing (lungs),
- excretion (intestines and colon) and
- fat production.
We certainly don’t mind if energy is burned as heat or used to build new protein, but we do mind if it is deposited as fat. There are an almost infinite number of ways that the body can dissipate excess energy instead of storing it as body fat.
By wrongly assuming that BMR, NEAT, TEF, and EPOC are constant over time , we conclude that increasing Calories Out depends solely on more exercise, which usually contributes to less than 5% of the game.
Both diet and exercise are important, but they are not equally important. If Diet is Luke Skywalker then Exercise is more of an Ewok. Consider a baseball analogy. Bunting is an important part of the game, but perhaps only 5% of it. Should we spend all our energy and practice time on the bunt? Obviously not. Putting too much emphasis on bunting hurts us because it does not leave time to practice more important parts of the game – pitching, hitting and fielding.
Exercise is the same. Sure, it’s important for a number of very good reasons. But we can’t expect it to produce significant weight loss. It’s a minor player. Emphasizing exercise detracts from the real issue of dietary problems.
Compensation: The hidden culprit
The fact that exercise never produces as much weight loss as we think has actually been well known in research for decades due to a phenomenon known as “compensation”—and there are two major mechanisms.
- You usually eat more if you exercise more
- You usually do less other activities if you exercise more
First, exercise usually makes us eat more. They don’t call it “working up an appetite” for nothing. A prospective cohort study of 538 students from the Harvard School of Public Health found that “although physical activity is thought of as an energy deficit activity, our estimates do not support this hypothesis.” For every extra hour of exercise, the kids ate an extra 292 calories. Caloric intake and expenditure are intimately related: increasing one will cause an increase in the other. This is the biological principle of homeostasis.
Second, exercise usually reduces non-exercise activity (NEAT). If you exert yourself all day, you are less likely to exercise in your free time. The Hadza, who were walking all day, reduced their physical activity when they could. In contrast, those North Americans who were sitting all day probably increased their activity when given the chance.
This principle also holds true in children. Students aged seven and eight years who received physical education in schools were compared to those who did not. The physical education group received an average of 9.2 hours per week of exercise through school, while the other group got none.
Total physical activity, measured with accelerometers, showed that there is no difference in total activity over the week between the two groups. Why? The PhysEd group compensated by doing less at home. The non-PhysEd group compensated by doing more when they got home. In the end, it was a wash. In addition, the benefit of exercise has a natural upper limit. You can’t exercise all day long to make up for a poor diet.
You can’t outrun a poor diet
Exercise is simply not all that effective in the treatment of obesity—and the implications are enormous. Vast sums of money are spent to promote physical education in school, the Let’s Move initiative, improved access to sports facilities, and improved playgrounds for children—all based on the flawed notion that exercise is instrumental in the fight against obesity.
If we want to reduce obesity, we need to focus on what makes us obese. If we spend all our money, research, time and mental energy focused on exercise, we will have no resources left with which to actually fight obesity. This is NOT to say that exercise is not healthy for you. It is like brushing your teeth. Good for you, do it every day, but don’t expect to lose weight.
We are writing a final examination called Obesity 101. Diet accounts for 95 percent of the grade, and exercise for only 5 percent when it comes to weight loss. Yet we spend 50 percent of our time and energy studying exercise. It is no wonder that our current grade is F.